There are many different methods for producing game balls. For example, balls for children are typically manufactured from plastic materials such as polyvinyl chloride. During manufacture, a liquid material is poured into a mold, where it solidifies to form a finished ball or at least one layer of the ball's outer cover. A typical method is disclosed in German Patent No. DE 27 23 625, which is hereby incorporated by reference herein in its entirety.
Higher quality balls, such as, for example, soccer balls for tournament play, typically have an outer layer assembled from separate panels that surround an inflatable bladder. Conventionally, there have been two kinds of game balls, a laminated ball and a hand-stitched ball. As disclosed in U.S. Pat. Nos. 4,333,648 and 6,503,162, the disclosures of which are hereby incorporated by reference herein in their entireties, an exemplary laminated ball includes a bladder made from air impermeable rubber. The bladder has a spherical hollow body into which compressed air is pumped through a valve. The ball further includes a reinforced layer formed by circumferentially winding a fiber, for example, a nylon filament, onto the entire surface of the bladder in order to reinforce the bladder and enhance mechanical properties of the ball, such as, for example, uniformity of size and weight distribution, sphericity, durability, and shape retention. A cover layer made of thin vulcanized rubber is then bonded onto the reinforcing layer, and an outer layer including a plurality of panels is mounted onto the cover layer. The cover layer typically serves to improve a bond between the panels and the ball's core. The panels are typically manufactured from artificial or natural leather. An end of the back of the leather panel is usually cut obliquely and a trench, having a substantially V-shape, is formed at a panel joint so that the panel wraps relatively smoothly around the ball.
A hand-stitched ball has a structure in which the bladder described above is surrounded by and is housed in an outer layer having a spherical shape formed by folding edges of a plurality of panels (also typically made from artificial or natural leather) toward the inside and sewing them together with a thread (usually about 10,000 deniers). Conventionally, a backing member formed by a plurality of woven fabrics is attached to the inside of the panel. For example, the woven fabrics can be bonded onto the inside of the panel with an adhesive such as a latex paste, thereby reinforcing the panel and providing additional cushioning during play. The panels described above, for example, pentagons and hexagons of a soccer ball, are typically produced as flat two-dimensional panels (not taking into account the thickness of the material).
FIGS. 1A-1C schematically illustrate the manufacture of such two-dimensional panels according to methods known in the art. Referring to FIGS. 1A-1B, layers 2, 3 are laminated to form a source material 5 of desired thickness. Two-dimensional panels 7 of desired size and shape are then cut out from the laminate 5 and, as shown in FIG. 1C, are sewn together or laminated onto a rubber bladder 9. As mentioned above, however, hand-sewing, as well as laminating, are complicated processing techniques that are difficult to automate. The more stitches or panel edges the ball has, the more costly it is to produce the ball.
Furthermore, the edges of the panels may cause delamination between the ball's component layers. Also, hand-stitched seams may be damaged after prolonged use. In particular, moisture may seep into the stitched seams, thereby disrupting the weight distribution of the ball so that it reacts unpredictably during play. Finally, the elastic properties of such assembled balls are not completely homogenous. For example, a soccer ball may react differently when it is kicked in the center of a panel as compared to when the player's foot contacts the seam between two panels.
In an attempt to minimize the disadvantages mentioned above, it has been known to decrease the number and increase the size of the panels, thereby reducing the number of stitched seams or border regions. A lower number of panels, however, leads to a structure, where each individual panel covers a larger section of the surface of the ball. Because the panels are two-dimensional, each panel needs to be curved to adapt to the rounded surface of the ball. Such shaping, however, may cause a considerable internal stress and strain on the panel. The larger the panel the greater the stress resulting from its curvature. Such stress may cause undesirable shape deviations and inhomogeneous elastic properties when the ball is inflated. To address these shortcomings, it has been proposed in, for example, French Patent Publication No. FR 2 443 850 and Japanese Unexamined Patent Publication No. JP 58-215335, the disclosures of which are hereby incorporated by reference herein in their entireties, to preform the panels prior to mounting them onto the bladder, to reduce the stress of the stitched seams or the border regions.
Known approaches, however, do not take into account the multi-layer composition of modern high performance balls, wherein one or more layers are arranged underneath the outer layer. During play, these additional layers are also subjected to considerable mechanical loads. Exemplary multi-layer systems for game balls are disclosed in European Patent Publication No. EP 0 894 514 and U.S. Pat. No. 6,306,054, the disclosures of which are hereby incorporated by reference herein in their entireties. Due to the high pressure inside the ball and load fluctuation during play, one or more interior layers may delaminate from the outer material, thereby compromising the ball's performance.
There is, therefore, a need for a game ball having larger outer panels with improved resistance to delamination of component layers and homogeneity of elastic properties.